Circuit for stabilizing frequencies of transmitter-receiver systems



Feb. 1, 1949. CANTELO 2,460,781

CIRCUIT FOR STABILIZINGFREQUENGIES OF TRANSMITTER-RECEIVER SYSTEMS FiledFeb. 27, 1945 Fig .1 kaAcm/vca FREQUENCV Mam/Mme 03c. MULT/PL/ER POWERAF 6: J 01 7 M1 I V A1 FZEQUE/VC) FQEOUENCV oer 5/ CHANGE Ml/LT/PA/ERJC- AFC 7- f WWW af' u mm 1.5 c N667? AMA & p/sa AMP AR E52 RECEIVER A JF551 A a I FREQUENCY CHANGER Fig 2 REACTAA/CE Fksoutwcr M00 LATOA? 0 c.MULT/PL/Ek POWER AMP AF CV 01 r 4 M1 A1 40w FREQ FREQUENCY CHANGER FREQ.awn/v 5? E FREQUENCY A F C MUL 7' IPA/ER FREQUENCY INVENTOR CHANGERHERBERT/Z (AA/r510 BY Wi 5 Patented Feb. 1, 1949 GIRCUIT FORSTABILIZ'ING FREQUENCIES F TRANSMITTER-RECEIVER: SYSTEMS Herbert.Reginald Cantelc, WrittIe, England, assignor to Radio Gorporationofi.America, a orporation of Delaware Application February 27, 19185.,Serial N0; 5735. 2.24;

In Great Britain October 7, 1943 Section 1, Public Law 690., August 8;.".946 Patentexpires October-7; 1963" This inventionrelates to frequencycontrolling and stabilizing means in radio apparatus. and the like,particularly in transmitter-receiver apparatus; that isradio apparatusand the like which may be used either as a transmitter or as. a re.-,ceiver. The invention is particularly suitable for use in such radioapparatus of the kind used forpoint-to-point operation on a common wave,and provides a means whereby the frequency of 18. Glaims- (01. 250- 6).

2: from Al isapplied'. These are the essential elements required fortransmission.

Again! in both figures, AR represents a receiving aerial, A2 a. radiofrequency amplifier to which. received energy: is applied, F03 afrequency changer inwhich received energy and a beat fre quency from F62are mixed to produce an intermediate: frequency, IFA an intermediatefrequency amplifier to which output from F033 is the oscillationsgenerated in the apparatus when pp DLa -discriminator to-which amactingas a transmitter may be stabilized, and D- fi d intermediate f q y" s ppe d whereby the apparatus when acting as a receiver fr W ch e d eq ySignal s demay be maintained in tune with a remote transrived. A3 anaudio frequen y amplifier, the O itter; in spite of some drift inthefrequency of put M r wh s pp i t y suita l utithe oscillatory energytransmitted by said translization devic (not shown). These are the esttesential. elements required for reception.

Though not exclusively applicable to angular II- fi r 0 r p nts astabilized (for velocity modulated systems, the invention is priexample, Crystal fi Osc a on enerama-rily intended for such systems.tor, M2 a frequency multiplier in which the freh inventionprovidesaisimple means for t, quency of oscillations from O2 is multiplied, F02taining the control and stabilization of frea frequency ha t whfrequency mu tiquency or tuning as: t case may be; 1; any pliedoscillations from MI and M2 are applied frequency within a band covered,or on any spot to p d a a r qu n y which s ppli d t wave within suchhand, without recourse having frequency cha r F0 get e With the reto behad to a variable intermediate frequency; ceived' radiofrequency'energy, e-p educe the in- According t t invention t widesttermediate frequency already referred to, FCl' a pact a radio apparatus,or the like, adapted f r frequency changer to which oscillations from Oluse alternatively as a transmitter or as a reg and (in Fig. 1)oscillations from M2 or (in Fig. 2) eel-Yer, includes an oscillationgenerator and a beat frequency from F04 are mixed to produce means forautomatically stabilizing the trans- F50; beat frequenfiyz M3repremitter oscillation generator and modulating the gents frequency n-13 1n W1110h the efrequency of oscillations produced th b in} quency ofthe oscillat ons generated in 02 is .cordance with Signing to betransmitted when multiplied or a harmomcselected, 03 1s a stable theapparatus is operating as a transmitter" or variable oscillationgenerator oflow frequency, in accordancewith drift in the frequency ofre- F frequency changer? in which oscillations sewed signals when theapparatus s operating EIOIn O3 and frequency multiplied oscillations asa receiver. iroin are mixed to produce a beat frcquencl The inventionis. illustrated in the drawing for These are essentia1e1e' whereof Fig.v1 illustrates the firstv arrangement ments forstablhzmg mtermeqlatefrequency of the invention, but is not the preferred ar- F mm e mngementand Fig 2 illustrates a preferred a} bilgzl 'lg thle frequency of theoscillations, gen r, rangemcntj Angular velocity modulation is as,- a gf i gim f f h sumedin both the systems illustrated. the, fig fi g 3312:A 1 z In both figures, OI represents an oscillation frequency may be apd o IFA l ea generator the oscillations from which are to beeonsidering, first, the arrangement of Fig. 1, modulated, or areactance. modulator r n r l the operation is as follows: valve winch 1Ssub ected to control by, for e During transmission the frequency changerample, audio irequencymgnals-AE from aiselirce FC'I' is excited from theoutput of the oscillator (not shown) and which serves: to; modulate theof and also from the output of the frequency genelfatcd' 0| ,1 Ml afrequency multiplier M2. Switch s is'on contact? and the ip ier toWhl-Qhv OSFIllBztlDD-S are difference frequencyiol. Mz o2 is extracted,and a d} phfier to which frequency used toexcite the intermediatefrequency ammultiplied: modulated oscillations. are applied, plifier IFAand limiter-discriminator DL The and AT a transmitting aerialtoxwhichtheoutput control valve CV and discriminator circuits DL of oscillationsfrom of increases, issuch .as to tend to reduce and thus restoretherfrequency of j oscillations from I oscillations of CI is made equalto 2 M2.02, and the mid-intermediate frequency will therefore: beM2.02.For the purpose of reception during which the power amplifier AI isswitched off at switch SI, a portion of the output of the frequencymultiplier Ml together with the output of the frequency multiplier M2.is used to excite the frequency changer F02, fromwhich the sum frequency(MI.OI+M2.02)' is extracted. This frequency is then mixed with theincoming'frequency in the frequency changer FC3 and the differencefrequency extracted. Switch S isnow on the. receiver-contact R and thesignal at this 'quency of oscillations from ojnusimilatlyjthe g sense ofthe. bias generated when thefre'quency the variable oscillator 03 ismixed with the out- .put frequency of themultiplier M3 in the frequencychanger FCA from which, as may be convenient, the sum or, the differenceof the two The nominal frequenc of .frequenc'ies may be extracted. Thisextracted freque'nc'y M3.0 2i03 is the reference frequency used for thestabilization of 01. Since the intermediate frequency and the frequencyto which the discriminator is tuned are constant it can be seenthat forany value of the frequency of Ol,

difference;,-frequency islthenused to excite IFA.

If the receiver and the'distant transmitter. are exactly in tune'thediif'erence frequency at F03 willbe (MI.Ol -l-,M2.0Z).MI.OI 0r M202.Since this is the mid-frequency of the intermediate frequencyamplifierIFA and limiter no frequency correcting bias will be generatedby DL. If, however; the frequency of the incoming signal decreases, thedifference frequency extracted from F03 will increase and thereforeproduce from discriminator DL a bias which will tend to decrease thefrequency of oscillation of Ol, and therefore also of the frequencymultiplier, MI. The frequency extracted from the frequency changer F03thus tends to remain constant, even if the incoming signalshould driftin frequency. In systems employinga narrow deviation band itisespeciallyimportantin'order to avoid distortion arising-in the detection of thesignallby the discriminator and-its rectifier that the mean frequencyapplied to the discriminator should remain substantially constant. Thecircuit means provided perm'it this end-to be achieved.

, The simple scheme described does not readily lend itself to the secondobject of the invention viz., the stabilization of the transmitteroscillator at any frequency within its hand, as it provides only forfrequency stabilization at one spot frequency of the transmitteroscillator. 'It is moreover subject to the disadvantage that theoutputcircuit of the frequency changer FCI is tuned to the rsame frequencyas-the'output circuit of the frequency multiplier M2. The outputcircuitof the frequencychanger F0] will therefore contain two components of thesame frequency, one derived from the frequency changing action and onearising from direct amplification of the frequency M202. Since thelimiter discriminator 'DL will respond to the larger of the two signalsit is necessary to make the component due to direct amplification ofM202 small in relationto .that due to frequency changing action, andthis "may bea matter of some dificulty to arrange.

Accordingly the slightly more complicated circuit arrangement shown inFig.2 is preferred. This incorporatesall the elements of Fig. 1 and thenecessary additional elements. The frequency of a the stable variableoscillator 03, which isof low frequency, maybe determined either by anL. C. circuit or by a CR circuit. The range of ably chosen, a suitableharmonic of the crystal oscillator may be combined with a suitable Valueof the frequency of the oscillator 03 to give a frequency which difiersfrom the frequency of the oscillator .Ol; by'aconstant amount equal tothe intermediate frequency; Thus, for example; let it'be assumed thatthe intermediate frequency is 4 mc./s. and that the oscillator Cl is tobe tunable over the range of 15 to 24 mc./s. Let it also be assumed thatthe frequency ofOZ is 1 mc./s. .and that the harmonic selector M3permits the selection of harmonics from the 10th to the 18th. Assumingthat the sum of the frequencies (03 +M3 .02) is extracted from F04 itcan readily bev seen that the ,frequency range to becovered by-03 isfrom 1 to 2 mgr/s. Thus with O! at 15 mc. s., M3.02will.be10 mc./s.,(M3.02+O3) will be 11 mc./s.; and tl'i edifference O'l (M3.02+O3) willbe 4 mc./s. With Ol at 24 mc./s., M392 will be 18 mc./s., and 03 will be2 mc./s., so that OI(M3.O2+O3)=24 (18+2)=4 mc./s. For some odd value ofthe frequency of Cl, say, 18.75 mc./ s., M302 willbe 13 Inc/s, and 03will be 1.75

mc./s., sothat V 7 ol (M3.02+Q3) '='18.75-'(13+1.75) =4 mc./s.

V Alternatively, if continuous variation of O! is not required, butmerely a selection of spot waves, 03 may be a crystal oscillator havinga harmonic selector covering any ,desired number of harmonics. over'a'ran'ge of the frequencies equal to the frequency of O2; ItWill thusact as a' Vernier to O2. 11f a. few spot waves only are required 03andFCfi maybe omitted and the output of M3 be fed directly to PC I;

' The frequency multiplier M2 .is of fixed frequency, and selects aharmonic 'of 02 equal to the intermediate -frequency. .The frequencychanger FCZ'istuned to avfrerq'ue'ncy (Ml.Ol+M2.02)

asin the case-of Fig. 1. 1 The frequency OI is not in-this circuitembodiment restricted in its relation-toM2.02.

' Since the frequency of O3 is small in relation to the harmonicfrequency M3-LO2',-with which it is combined;a-smalrpercentage drift in03 will represent a much smaller percentage drift in the combinedfrequency (03 +M3.02)and will therefore have negligible effect on thestability of the y te If. f 1 l I 1 An advantage of the system in boththe-simple and preferred ar'rangemerits 'is that "the output of thefrequency multiplier M2 may, by suitable switching, be used for thepurpose of alignment *of the:intermediatc'frequency stages, without theuse of an external source'of frequency; I ."WhatiS claimed-is":

1. A radio or like apparatus adapted for use estates alternatively as atrans lming bs'ci-ll" mission, a frequency "changer for p od-uc'ing anintermediate frequency frolii received 'sig'n-ljfriequency andoscillations derived from said oscillat tion generator, means forproducing a ire quen'cy controlling potential variable in sign andmagnitude in accordance with departures om a desired frequency ofthefioutpu't from said gen- "orator, means ror rcducin' a secondfrequency controlling pdten'tial variable in and magni tude in"accordance with departures frdmthe frequency "of received signalfrequency requisite to "maintain a desired mean frequenc o'fjsaid inter-"mediate frequency, "a frequency 'controlling'derice for saidoscillation generator operable under control of said first frequencycon-trolling potential to stabilize the frequency of said generator orunderjcon't'rol of said second frequency controll lng potential to varythe frequency ofsaid generator, thereby to stabilize said intermediatefrequency. I

2. Apparatus "as claimed in claiml, including a stabilized oscillationgenerator and a second frequency changer and wherein said firstfrequency controlling potential "is derived from a first frequencycontrolling beat frequency produced by mixing oscillations derived fromboth said gener'ators in said second frequency changer coupled theretoand to said first oscillation generator-Ln,

3. Apparatus as claimed in claim 1, includinga stabilized oscillatorgenerator, a second frequency changer coupled thereto and to said "firstoscillation generator, a coupling between said second frequency changerand said frequency changer and wherein said second frequency controllingpotential is derived from said intermediate frequency "and wherein saidintermediate frequency is produced by mixing a second frequencycontrolling beat frequency with said received signal frequency in saidfirst frequency changer, said second frequency controlling beatfrequency being produced by mixing oscillations derived from both saidgenerators insaid second frequency changer.

4. A radio or like a paratus adapted foruse a'lternatively as atransmitter or as a "receiver apparatusis operating as "a transmitter, asecond oscillation enerator, means for deriving a first automaticfrequency controlling beat frequency from oscillations generated by bothsaid generators, means for deriving a 'iirst automatic frequencycontrolling potential from said first automatic frequency controllingbeat frequency and means for applying said potential to said firstgenerator so as to maintain the frequency of oscillations generatedthereby substantially constant, and, for use when said apparatus isoperating as a receiver, said second oscillation generator, means forderiving a second automatic fre quency controlling beat frequency fromoscilla tions generated by both said generators, means for deriving anintermediate frequency from said second automatic frequency controllingbeat frequency and said received oscillatory energy, means for derivinga second automatic frequency controlling potential from saidintermediate frequency, and means for applying said potential tosaidffirst eeneiatorseas to vary the re-queasy of the oscillationsgenerated thereby, by varying the frequency *of said second automaticfrequency controlling beat frequency, ll'dmaliritji-n said intermediatefrequency substantially con stant spite of drifts in the frequencyof-said received os'cillat-oryenergy V L 5. ,A radiogor like'apparatusadapted for use alteinativelyas a transmitter or s a recerverand having a first oscillation generator; means for modulatingoscillations from "stiid generator in accordance with signals to betransmitted, means for transmitting modulated oscillations, and meansfor receiving oscillatory energy from a remote station includin for usewhen -said rap paratus' operating as a transmitter, a first stabilized.oscilia'tion generator, a second stabili'zed, variable, oscillationgenerator, :inefa'ns for deriving a stable beat frequency fromoscillations enerated by both said stabilized oscillation generators,means for deriving a first automatie frequency controlling beatfrequency from said stablebeat frequency and oscillations from saidfirst generator, means for deriving a first automatic frequencycontrolling potential from said first automatic frequency controllingbeat frequency, and means for applying said potential said firstgenerator so as to maintain the firequency of oscillations generatedthereby substantiallyaconstan-t, and, for use when said apparatus isoperating as a receiver, said-firststabilized-oscilla-tion generator,means for deriving a second automatic frequency controlling beatfrequency from oscillations generated by said first andfirst stabilizedoscillation generatorsnieans for "deriving an intermediate frequencyfrom said second automatic "frequency controlling beat frequency andsaid received oscillatory energy, means for deriving a second automaticfrequency controlling the first beat frequency is derived from themixii-1g of oscillations from the first generator without frequencymultiplication with oscillations from said second generator.

7. Apparatus as claimed in claim 5, whercin the modulated"oscillationsare subjected to frequency'inultiplicati'on before transmission "and thefirst automatic frequency controlling beat frequency is derived from themixing of oscillations from thefirst generator without frequencymultiplication with the stabilized beat frequency.

8. Apparatus as recited in claim 1 including a stabilized oscillationgenerator, 2. frequency increaser coupled therewith wherein oscillationsproduced by said stabilized oscillation generator are subject tofrequency multiplication and harmonic selection, said first meanscomprising a frequency changer coupled to said first oscillationgenerator and said frequency increaser wherein oscillations from saidfirst mentioned oscillation generator are mixed with oscillations fromsaid frequency increaser for the production of energy of beat frequencyfrom which said first frequency controlling potential is derived.

,9. ,Apparatus as recited inclaim 1 including a stabilizedoscillationgenerator, a first frequency oscillations are subject to frequencymultiplication before transmission, a second frequency mulsaid secondmeans for producing said second frequency controlling potential.

10'' Apparatus as recited in claim 1 including :a stabilized oscillationgenerator and a stabilized variable frequency oscillation generator, afrequency changer coupled with said last two generators for producingenergy, of abeatfre'quency and of constant frequency, and wherein saidfirst means includes a frequency changer coupled with said last namedfrequency changer and with said first oscillation generator forproducing energy of :a second frequency controlling beat frequency fromwhich said'first frequency controlling potential is derived. 7 V

'11. Apparatus as recited in claim 1 including a stabilized oscillationgenerator, a second fre- -quency changer coupled to said stabilizedoscillation generator and to said first oscillation generator forderiving energy of frequency controlling beat frequency; and whereinsaid second means includes a coupling between said second frequencychanger and said first frequency changer which is excited by receivedsignals for producing energy of a second frequency controlling'beatfrequency from which is derived said second frequency controllingpotential.

'12 Apparatus as recited in claim 1 including a stabilized oscillationgenerator, a 'second' frequency changer coupled therewith and with saidfirst named oscillation generator, a, frequency 'multiplier in each ofsaid last two named cou- 'plings, and wherein said second named meansincludes a coupling between said second frequency changer and said firstnamed frequency changer which is excited by;received signals forproducing energy of a frequency controlling beat frequency from whichsaid second mentioned fre-.

quency controlling potential is derived.

13. Apparatus as recited in'claim 1 including a source of signals and acoupling between. said source of signals and said frequency controllingdevice for modulating the oscillations generated bysaid first generatorin accordance with signals.

- 14. ApDf ratus as recited in claim 1 wherein said 15. Apparatus asrecited in claim 4 including a V f requencymultiplier coupled to saidfirst oscilla- ,ticn generator in which multiplier the modulatedautomatic 11 19? cflupled to said second oscillator, said third meansincluding a frequency changer coupled to said modulat'edoscillator andto said second frequency multiplier so that said first automaticfrequency controlling beat frequency is derived by mixingoscillationsfrom said second generator multiplied in frequency with oscillationsfrom said first oscillation generator.

16. Apparatus as recited inclaim 4 including a frequency multipliercouple'd to said modulated oscillation generator, a frequency multipliercoupled to said second oscillation generator and wherein said means forderiving said second automatic frequency controlling beat frequencyincludes a frequencychanger coupled to both of said frequencymultipliers. V

17. Apparatus as recited in-claim 5 including a frequency multipliercoupled to said modulated oscillation generator to subject the modulatedoscillations to frequency multiplication before transmission, a secondfrequency multiplier coupled to said first stabilized oscillationgenerator, and wherein said fourth means includes a frequency changercoupled to said last mentioned frequency multiplier and to said secondstabilized oscillation generator for deriving said first stabilized beatfrequency.

18., Apparatus as recited in claim 5 wherein said means forderiving saidsecond automatic frequency controlling 'beat'frequency includes afrequency changer and frequency multipliers coupling said firststabilized oscillation generator and said first oscillation generator tosaid frequency changer wherein isderived said second frequencycontrolling beat frequency. HERBERT REGINALD CANTELOH REFERENCES CITEDThefollowing references are of record in the file of this patent:

v UNITED STATES PATENTS Number f Name Date 2,228,815 Deerhake Jan. 14,1941 2,276,008 1 Armstrong Mar. 10, 1942 2 ,317,547 McRae Apr. 27, 19431 2,333,719, Heroldv Nov. 9, 1943 2,363,835; Crosby Nov. 28, 19442,379,395 Ziegler et al. June 26, 1945 2,380,288 Bligh July 10, 19452,407,212 Tunick Sept. 3, 1946 2,408,791 Magnuski Oct. 8, 1946 2,408,826Vogel Oct. 8, 1946 i FOREIGN'PATENTS- Number Country Date 551,472 IGreat Britain Feb. 24, 1943

